Gas turbines are well-known in the art. It is an ongoing quest within the gas turbine field to increase the thermal efficiency of the gas turbine cycle. One way this has been accomplished is via the development of increasingly temperature-resistant materials, or materials that are able to maintain their structural integrity over time at high temperatures. For example, single crystal (SX) alloys have been developed that are able to withstand higher working temperatures. This is believed to be due, in part, to the fact that single crystal structures have the ability to withstand creep at higher temperatures than polycrystalline turbine blades due to the lack of grain boundaries. Grain boundaries are an area of the microstructure where a number of defects and failure mechanisms start that may lead to the occurrence of creep. The lack of these grain boundaries in directionally solidified single crystal materials, for example, reduces the likelihood of creep.
Brazing is a method commonly used to coat, repair, add buildup to, or join components, such as superalloy components. Typically, brazing involves melting a braze material at a temperature less than a liquidous temperature of the base component and allowing the material to solidify to become integral with the base component. One limitation of brazing is that the final brazed material (hereinafter “brazement”) is typically much weaker than the component being brazed. Thus, brazing may not be fully beneficial in all situations, such as repairs to the most highly stressed areas of a component. This issue is heightened with the enhancement (e.g., coating, repair, or buildup) and joinder of SX materials, for example. When polycrystalline superalloys are used as the braze material to enhance or join SX materials, the brazement will typically not crystallize in the same orientation as the base SX component. This results in a brazement that is weaker than the base component. Further, the use of SX materials in a braze material to join or repair SX materials is problematic because such a brazing process is highly intensive and requires extremely tight process controls.
In addition to SX materials, titanium-based materials, such as TiAI materials, are also becoming increasingly used in gas turbines, particularly with low pressure blades of the turbine. The Ti material is typically half as dense as comparable Ni-based alloy materials yet exhibits excellent temperature stability and corrosion-resistance. However, with Ti-based materials, enhancement or joinder by brazing also becomes very challenging due to brittle contact between the surfaces of the braze material and the titanium-based component. Generally, the brittleness of a Ti-based substrate renders it difficult for a strong interface to be formed between the braze material and the Ti-based substrate.
Moreover, despite the improved thermal properties of the above-discussed materials, the gas turbine environment is notably harsh. Thus, damage and deterioration of the components of the gas turbine still occur. For example, the surface of a component may become cracked due to thermal cycling or thermo-mechanical fatigue, or the component may erode as a result of impacts with foreign objects and corrosive fluids. Furthermore, such components may even be damaged during manufacturing operations prior to entering service. Because the cost of gas turbine components continues to be relatively high, repair of a damaged or degraded component is preferred over replacement of the component. New techniques for improving the repair and enhancement of these improved materials are thus needed.